1. Field of the Invention
The present invention relates to a transistor with an internally impedance matched circuit for use in the microwave band and, more particularly, to such an internal matching transistor incorporated in the same package with a stabilizing circuit for preventing unwanted oscillation.
2. Description of Related Art
High output transistors operable in the microwave band used in satellites and mobile communications stations typically comprise semiconductor components and a matching circuit in the same package. FIG. 8 shows the internal design of such a high output transistor, and FIG. 9 is an equivalent circuit diagram for the high output transistor shown in FIG. 8.
In the high output transistor 100 shown in FIGS. 8 and 9 there are a plurality of semiconductor elements 101, which are field effect transistors. An input impedance matching circuit 102 is disposed toward the microwave signal input side, and an output impedance matching circuit 103 is disposed toward the output side, of each semiconductor element 101.
Bonding wires connect the semiconductor elements 101 to the input impedance matching circuit 102 and output impedance matching circuit 103, the input impedance matching circuit 102 to package lead-throughs 104, and the output impedance matching circuit 103 to package lead-throughs 105.
The matching circuit in this type of internally impedance matched transistor circuit having a semiconductor element inside the same package typically includes striplines connected in series between the inputs and outputs of the semiconductor element and the wire inductance. The matching circuit is therefore usually a low-pass filter type circuit, and it is difficult to achieve a high-pass filter matching circuit. A low-pass filter matching circuit is a high impedance device in the frequency band in which a high frequency transistor is used, and a low impedance device in a low frequency band. Impedance is therefore also low in circuits external to the package at low frequency, the reflection coefficient increases at the reflection plane in a 50.OMEGA. system and the stability coefficient is low. The system is therefore susceptible to low frequency oscillation.
Recent development of high output transistors has tended towards further increasing output, thus also increasing device size. As device size increases, input impedance drops and low frequency oscillation problems during high frequency band operation become even greater.
Internal matching circuits and transistors are also typically used with the top of the package sealed by a metal conductor or ceramic cover. This makes it difficult to add a new stabilization circuit internally to the package when anti-oscillation measures adding a stabilization circuit externally to the package are not effective.
It is to be noted that Japanese Patent Laid-open Publication No. 63-86904 teaches an internally impedance matched, high output field-effect transistor in which an anti-oscillation resistor is used between parallel connected transistors to suppress unnecessary oscillation in odd modes.